1. Field of the Invention
This invention generally relates to a method and apparatus for surface coating a relatively dense fiber glass blanket to form a duct liner product and the so-formed duct liner and more specifically, to an on-line method and fabrication apparatus for applying a surface coating to one facing surface and the edge surfaces of a fiber glass blanket to provide a fiber glass duct liner product wherein all surfaces exposed to air traveling through the duct are coated with an applicable coating.
2. Description of the Prior Art
It is well known and standard practice to use a relatively dense layer of flexible fiber glass as an internal liner for sheet metal ductwork in heating, ventilating and air conditioning applications. Such liners function both as an insulation to conserve the temperature of the air within the duct and to prevent condensation on the duct exterior surfaces, and at the same time, provide efficient sound absorption to control airborne noises. In that the fiber glass liner is on the inside of the duct and therefore adjacent the high velocity air, it is a requirement of certain federal, state, local and trade association regulations that the liner meet certain standards for use in such environment.
One of the typical standards the liner must exhibit is a resistance to erosion by the air flowing through the duct. Such standard requires that duct liners shall not break away, flake off or show evidence of delamination or continued erosion when air is passed through typical sections at a velocity of 21/2 times rated velocity but not less than 5000 ft/min. Therefore, to accommodate such standard it is typical for fiber glass duct liner manufacturers to coat the face of the fiber glass blanket which will be exposed to the air with a coating that prevents erosion of the glass fibers from such surface under the above established conditions. Such coatings can be a rubberized or plastic type material that is applied onto such surface of the fiber glass and when cured forms a tough skin on such surface. Alternatively, or in conjunction therewith, a fabric layer such as a Chicopee material can be adhered to such surface of the fiber glass.
Also, as is typical in the industry, the manufacturers of fiber glass duct liner provide the heating, ventilating and air conditioning contractor, installing the ducts, with rolls of fiber glass duct liner in lengths of approximately 100 feet and in standard widths varying from between 2 to 5 feet. The contractor in turn, often times in an automatic coil line, adheres the fiber glass duct liner to a surface of the sheet metal with the coated side of the duct liner being exposed, thereafter trimming the sheet metal and duct liner combination to standard lengths which are thereafter formed into length having an "L" shaped configuration. Two such L's placed in opposed relationship and joined along their mating seams thereby provide a length of duct with the fiber glass liner providing the inside surface. As will be more clearly explained hereinafter, each end of a duct, as formed above, may have an exposed edge surface of the fiber glass liner.
Heretofore it has not been the practice of fiber glass duct liner manufacturers to coat that portion of the liner which forms this edge surface; however, as the thickness of such edge is not always consistent, because of the variations in the thickness of the fiber glass liner, a joint of two such ducts may expose a portion of the uncoated edge surface to the air flow and provide a potential area of erosion. It has thus been the practice of the contractor, to comply with the appropriate standards, to coat such exposed edges of the fiber glass. Normally this is done while the L-shaped lengths are serially stacked in a manner to expose the edges. This coating typically has been the same adhesive that was applied to adhere the fiber glass to the sheet metal and can be done manually, as with a spray gun, brush, or roller, while the L-shaped lengths are in their stacked condition. However, it is evident that this requires further labor and handling by the contractor and can result in a rather messy, unattractive and potentially hazardous environment where the adhesive is indiscriminately sprayed or applied. Further, such adhesive coating may not, in fact, satisfy erosion standards.